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  #1  
Old 04-09-2006, 08:15 PM
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300sd cruise amp removal - advice pls for newbie

Hi

I was lucky enough to find a 300sd cruise amplifier at a wreckers for $40. I was going to try and replace mine as I have no cruise. After some fun, I got all the trim out to find the amplifier - am I correct that if I remove the bolt ABOVE the amplifer, the metal plate to which the amplifer and another electrical whiz-bang are bolted will come out?

Otherwise I cannot figure out how to remove the phillips screws holding the amplifier to the mounting plate.

Thanks if someone can provide advice

Ritchie Leslie

300sd 125k km (new toy) 1983
VW jetta diesel 175 k km 1992
2001 Mazda MPV LX
1971 David Brown 990 3.3L diesel farm tractor

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  #2  
Old 04-09-2006, 08:26 PM
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Location: Blue Point, NY
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Quote:
Originally Posted by 300sdToronto
am I correct that if I remove the bolt ABOVE the amplifer, the metal plate to which the amplifer and another electrical whiz-bang are bolted will come out?

Otherwise I cannot figure out how to remove the phillips screws holding the amplifier to the mounting plate.
You are correct. Any you need to be a contortionist to get at that nut.

The metal plate is removed with the black warning buzzer and the cruise amp attached.
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  #3  
Old 04-09-2006, 09:09 PM
Jeremy5848's Avatar
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Location: Sonoma Wine Country
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Cruise control removal

I just removed my cc "brain." In the 1985 300DT (123) it is attached with two Phillips screws. One was possible, the second I could not even see, much less get out. I finally bent the tabs of the aluminum box and carefully slid the pc board out, leaving the box in place.

Only problem since is that I can't find anything wrong with the board. It's clean, with no cracked traces or fried components. There are some small electrolytic capacitors that I'm gonna test as they sometimes go bad. (My unit works but is flakey -- it drops out for no reason from time to time, or sometimes refuses to work at all. Once it stuck in "accelerate" and I had to manually shut it off as it was gonna speed up forever.)

I plan to check and clean all of the cables and connectors in the system, see if I can find the source of the trouble. I hate to spend big bucks replacing the "brain," especially it it turns out not to be at fault.

By the way, the pc board is full of American-made components, including several amplifier chips made by my former employer, National Semiconductor. I'm doomed!!!

Attached for the curious is an image of the pc board.

Jeremy in Santa Rosa, California
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300sd cruise amp removal - advice pls for newbie-cc_1164.jpg  
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  #4  
Old 04-09-2006, 10:55 PM
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Location: PA
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Make a bench that is the same height as the door sill. Then you can lay on that bench and the door sill without breaking your back to R&R the cruise control computer.

Before U put the computer back in, epoxy the bolt that mounts the computer into the hole the bolt goes thru and it will be easy to start the nut and U won't have to hold a wrench on the bolt to tighten the nut.

P E H
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  #5  
Old 04-10-2006, 12:59 AM
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Location: mesa az
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Quote:
Originally Posted by Jeremy5848
I just removed my cc "brain." In the 1985 300DT (123) it is attached with two Phillips screws. One was possible, the second I could not even see, much less get out. I finally bent the tabs of the aluminum box and carefully slid the pc board out, leaving the box in place.

Only problem since is that I can't find anything wrong with the board. It's clean, with no cracked traces or fried components. There are some small electrolytic capacitors that I'm gonna test as they sometimes go bad. (My unit works but is flakey -- it drops out for no reason from time to time, or sometimes refuses to work at all. Once it stuck in "accelerate" and I had to manually shut it off as it was gonna speed up forever.)

I plan to check and clean all of the cables and connectors in the system, see if I can find the source of the trouble. I hate to spend big bucks replacing the "brain," especially it it turns out not to be at fault.

By the way, the pc board is full of American-made components, including several amplifier chips made by my former employer, National Semiconductor. I'm doomed!!!

Attached for the curious is an image of the pc board.

Jeremy in Santa Rosa, California

try resoldering the board. there alot of cold solder joints on these due to being flow soldered.
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  #6  
Old 04-10-2006, 08:49 AM
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Location: Matthews, NC
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I have found that most intermittant problems with automotive electronic devices is the solder joints where the plug-in socket or pins is soldered to the board. This is usually caused by the weight of the cable bouncing around as you drive. If you look very close using a magnifying glass, you will see hair line crackes in the joint. They usually look like a circle around the pin. Also look at the pins around any heavy componts like relays, etc. They will also crack. Sometimes on double layered boards the crack will be hidden from view by the componts. Carefully resolder all the joints mentioned above even if you don't see anything. This trick has fixed many expensive electronic parts that usually get replaced.
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  #7  
Old 04-10-2006, 09:15 AM
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Location: RI shore
Posts: 2,937
Quote:
Originally Posted by 300sdToronto
Hi

I was lucky enough to find a 300sd cruise amplifier at a wreckers for $40. I was going to try and replace mine as I have no cruise. After some fun, I got all the trim out to find the amplifier - am I correct that if I remove the bolt ABOVE the amplifer, the metal plate to which the amplifer and another electrical whiz-bang are bolted will come out?

Otherwise I cannot figure out how to remove the phillips screws holding the amplifier to the mounting plate.

Thanks if someone can provide advice

Ritchie Leslie

300sd 125k km (new toy) 1983
VW jetta diesel 175 k km 1992
2001 Mazda MPV LX
1971 David Brown 990 3.3L diesel farm tractor
you are right, those screws are difficult (but not impossible) to access to remove. I slotted my bracket so I don't have to touch the one screw closer to firewall that's really difficult.
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  #8  
Old 04-10-2006, 09:37 AM
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Join Date: Mar 2006
Posts: 545
More on my cruise

My thanks to all who provided advice.

While I have the dash opened up again I was also going to test all the cruise wiring for continuity and proper grounds. My stop lights work fine, before anyone asks!

How does one test the actuator? I did clean the contacts on the wiring connector for it beside the tach amp, but it made no difference. I did put some kleenex in the top of the tach amp and fixed by juddering tach needle!

I can't figure out how to observe cruise amp operation with a DVM under the hood unless you sit on top of the engine while someone else drives the car down the road at 40 mph!!


Ritchie L
83 300sd 125,000 kms
92 Jetta diesel
990 DB farm tractor
2001 Mazda MPV
forgot the old Gravely walking tractor with indestuctible Kohler engine!
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  #9  
Old 04-11-2006, 12:24 AM
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Location: Santa Monica, CA
Posts: 2,053
actuator test.

http://gdl-online.com/test023.html

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